Abstract The isotopic compositions of oxygen ( δ 18 O) and hydrogen ( δ 2 H) are widely used to locate the geographical origin of biological remains or manufactured products. In this paper, we analyse the distributions of δ 18 O and δ 2 H in tap waters sampled across France, and in precipitation interpolated with the Online Isotopes in Precipitation Calculator and modelled with the isotope-enabled ECHAM6-wiso model. Our aim is to provide isoscapes usable in archaeology and forensics and evaluate whether the modelled data could be surrogates for measured ones. The δ 18 O and δ 2 H in the 396 tap waters sampled varied spatially within a range of 10‰ and 77‰, respectively. Their consistent distributions followed rules summarized by the effects of altitude and distance from the coast. Their variations along the year were small. Therefore, the database provides a solid reference for δ 18 O and δ 2 H of the water supply system at the regional scale. The areas with the most uncommon oxygen and hydrogen isotopic compositions (Atlantic coast south of Brittany and the highest elevations in the Alps) are the most accurately traceable areas in provenancing studies. The isotopic compositions of modelled precipitation have the same spatial distributions but different absolute values from those of tap waters. Therefore, our results favour the use of statistical isoscapes rather than general circulation model-based isoscapes in provenancing studies.